Production of hydrocarbons from loosely or unconsolidated and/or fractured formations often produces large volumes of particulate material along with the formation fluids. These particulates can cause a variety of problems. Gravel packing is a common technique for controlling the production of particulates (e.g. sand).
Gravel pack completion involves lowering a screen on a workstring into the well bore and placing the screen adjacent to the subterranean formation. Particulate material, collectively referred to as “gravel”, and a carrier fluid is pumped as a slurry down the workstring where it exits through a “cross-over” into the well annulus formed between the screen and the well bore.
The carrier liquid in the slurry normally flows into the formation and/or through the screen, itself, which, in turn, is sized to prevent gravel from flowing through the screen. This results in the gravel being deposited or “screened out” in the annulus between the screen and the well bore and forming a gravel-pack around the screen. The gravel, in turn, is sized so that it forms a permeable mass which allows produced fluids to flow through the mass and into the screen but blocks the flow of particulates into the screen.
It is often difficult to completely pack the entire length of the well annulus around the screen. This poor distribution of gravel (i.e. incomplete packing of the interval) is often caused by the carrier liquid in the gravel slurry being lost into the more permeable portions of the formation interval which, in turn, causes the gravel to form “sand bridges” in the annulus before all of the gravel has been placed. Such bridges block farther flow of slurry through the annulus thereby preventing the placement of sufficient gravel (a) below the bridge in top-to-bottom packing operations or (b) above the bridge in bottom-to-top packing operations.
Alternate flow conduits, called shunt tubes, alleviate this problem by providing a flow path for the slurry around sand bridges. The shunt tubes are typically run along the length of the well screen and are attached to the screen by welds. Once the screen assemblies are joined, fluid continuity between the shunts on adjacent screen assemblies must be provided. Several methods have been attempted to provide such continuity.
U.S. Pat. No. 6,409,219, by Broome et al. describes a system wherein shunts on adjacent assemblies aligned when the correct torque is applied to join the assemblies. Alignment marks are included on the assemblies to indicate when the correct torque has been applied.
U.S. Pat. No. 5,341,880, by Thorstensen et al. describes a sand screen structure assembled from a plurality of generally tubular filter sections that may are axially snapped together in a manner facilitating the simultaneous interconnection of circumferentially spaced series of axially extending shunt tubes secured to and passing internally through each of the filter sections. In an alternate embodiment of the sand screen structure the shunt tubes are secured within external side surface recesses of the filter section bodies.
U.S. Pat. No. 5,868,200, by Bryant et al. describes an alternate-path, well screen made-up of joints and having a sleeve positioned between the ends of adjacent joints which acts as a manifold for fluidly-connecting the alternate-paths on one joint with the alternate-paths on an adjacent joint.
Another configuration known in the art uses screen assemblies having shunts that stop a certain length from the ends of the screen assemblies to allow handling room when the screen assemblies are joined together. Once the screen assemblies are joined, their respective shunt tubes are linearly aligned, but there is a gap between them. Continuity of the shunt tube flow path is typically established by installing a short, pre-sized tube, called a jumper tube, in the gap. The jumper tube features a connector at each end that contains a set of seals and is designed to slide onto the end of the jumper tube in a telescoping engagement. When the jumper tube is installed into the gap between the shunt tubes, the connector is driven partially off the end of the jumper tube and onto the end of the shunt tube until the connector is in a sealing engagement with both tubes. The shunt tube flow path is established once both connectors are in place. A series of set screws engage both the jumper tube and shunt tube. The screws are driven against the tube surfaces, providing a friction lock to secure the connector in place. This connection is not very secure and there is concern that debris or protruding surfaces of the well bore could dislodge the connectors from sealing engagement with the tubes while running the screens into the well bore. Therefore, a device called a split cover is typically used to protect the connectors. A split cover is a piece of thin-gauge perforated tube, essentially the same diameter as the screen assembly, and the same length as the gap covered by the jumper tubes. The perforated tube is spit into halves with longitudinal cuts. The halves are rejoined with hinges along one seam and locking nut and bolt arrangements along the other seam. The split cover can be opened, wrapped around the gap area between the assemblies, and then closed and secured with the locking bolts. Split covers have several disadvantages: they are expensive, they must be sized to fit a particular gap length and therefore care must be taken to insure that the correct lengths are sent to the well site, they are awkward to install, and they are not very robust and can suffer damage when they are run into the well.